Process Controller Type 8693 - Bürkert 8692 Operating Instructions Manual

8

PROCESS CONTROLLER TYPE 8693

In the case of process controller Type 8693 the position control mentioned in chapter "7 The position controller
Type 8692" becomes the subordinate auxiliary control circuit; this results in a cascade control. The process
controller in the main control circuit of Type 8693 has a PID function.
The process set-point value (SP) is specified as set-point value and compared with the actual value(PV) of the
process variable to be controlled.
The position sensor records the current position (POS) of the pneumatic actuator. The position controller
compares this position actual value with the set-point value (CMD) which is specified by the process controller.
In case of a control difference (Xd1), a pulse-width modulated voltage signal is sent to the actuating system
as an actuating variable.
If there is a positive control difference in single-acting actuators, the aeration valve is controlled via output B1.
If the control difference is negative, the bleed valve is controlled via output E1. In this way the position of the
actuator is changed until control difference is 0. Z2 represents a disturbance variable.
SP
+
Process set-
point value
Figure 6: Signal flow plan of process controller
24
Xd1
CMD
+
-
Positioner
Position control circuit
Position
CMD
Xd2
control
-
circuit
Process
controller
PV
english
Z1
B1
P
K
E1
Continuous
Control system
valve
Solenoid
valves
POS
Position sensor
Z2
Valve
opening
Process
Transmitter
Type 8692, 8693 REV.2
Process controller Type 8693
Valve
opening
Process variable